Whatever refrigerant is chosen will always have to be a balance between several factors, the availability and cost of the refrigerant (and the associated equipment), the system energy efficiency, the safety and convenience of applicability, environmental issues and many more.
The perfect refrigerant does not exist, and is unlikely to come into existence. Choices will therefore include the existing low GWP refrigerants (e.g. R-717, R-744 or HCs) and the newly applied or developed chemicals. Many new alternatives are proposed which create a challenge in finding the right refrigerant for each application. One aspect of particular importance is that refrigerants with low direct impact on climate change are often flammable to some extent. With new refrigerant characteristics comes the need for new technology development and increased need for training.
21 refrigerants obtained standardized designations and safety classifications since the 2010 RTOC assessment report, including one new molecule: HCFC-1233zd(E). Approximately a quarter of the new refrigerants are blends which are replacements for HCFC-22. Of the new refrigerants twelve are blends of saturated HFCs and unsaturated HFCs (HFOs) of which seven blends are with class 2L flammability.
Domestic appliances
Globally, new refrigerator production conversion from use of ODS was essentially completed by 2008. HC-600a or HFC-134a continue to be the refrigerant option for new production.
It is projected that by 2020 about 75% of new refrigerator production will use HC-600a (possibly with a small share applying unsaturated HFC refrigerants) and the rest will use HFC-134a.
Initial efforts to assess the use of HFC-1234yf in domestic refrigeration have begun, but they are not being pursued with high priority, due to cost implications and flammability.
The heat pump clothe (laundry) dryer (HPCD) sales using HFC-134a are fastly growing in the EU. HPCDs using R-407C and HC-290 have also been introduced. Alternative refrigerant solutions that are being explored include R-744, HC-600a and low GWP HFCs.
Commercial refrigeration
In commercial refrigeration stand-alone equipment, hydrocarbons (HCs) and R-744 are replacing HFC-134a and R-404A and represent a significant market share in Europe and in Japan.
Because of their high GWP, R-404A and R-507 are seen as refrigerants in many non-Article 5 countries as refrigerants to be replaced and, depending on the refrigeration capacities, hydrocarbons, R-744 or HFC refrigerant blends with lower GWP are the current chosen options.
In supermarkets in Europe, two-stage CO2 systems are recognized as viable option especially in moderate temperature countries. The technology is now spreading to other areas and development of concepts for hot climates is ongoing.
Plug-in units with air and/or water cooled condensers are gaining market share. Particularly in the USA, distributed systems (condensing units with water cooled condensers installed in the sales area) are also installed in large numbers.
Industrial systems
R-717 is widely used in industrial systems, but its adoption as a low GWP alternative to HCFC-22 in Article 5 countries is not universal due to safety concerns. The key requirements to facilitate this transition are education and training of designers and operators.
Although HFCs are technically feasible for large industrial systems, the market sector is extremely cost sensitive and more expensive refrigerants are not favoured due to the large charge quantity required.
Transport refrigeration
Low-GWP candidates for transport refrigeration include R-744, hydrocarbons, and HFC blends; however, various challenges are currently preventing them from widespread use. Intermodal container applications are at the forefront of developments; here the R-744 based system is available.
In the case of a regulation banning the use of refrigerants above a certain GWP level (as in the EU), HFC blends will likely play a role in the 2020 timeframe as a retrofit to R-404A and (possibly) HFC-134a: their GWP is significantly lower and performances are close.
Cryogenic and eutectic systems consist of potentially HFC-free stationary units and periodically recharged vehicle systems; they can be used on some transport routes.
Air-to-air air conditioners and heat pumps
HCFC-22 is still widely used in new and existing systems in Article 5 countries and to some extent in existing systems in non-Article 5 countries.
The majority of new systems using an alternative to HCFC-22 use R-410A; some others are using R-407C, HFC-134a, HC-290 and HFC-32.
There are a growing number of alternatives which have a medium to low GWP and are flammable that are being considered and evaluated by research entities and enterprises, meaning there is some degree of uncertainty over future selection of alternatives.
For water heating heat pumps most systems commercialised today make use of R-410A, HFC-134a, R-407C, HC-290, HC-600a, R-717 or R-744. The majority of new equipment uses R-410A.
In some Article 5 countries HCFC-22 is used. There are no technical barriers for replacing HCFC-22 by a non-ODS refrigerant in new systems. The main parameters in the selection of alternatives when switching over from HCFC-22 are efficiency, cost effectiveness, economic impact, safe use and easiness of use.
HFC-32 and other medium and low-GWP HFC blends are under way to become commercially available. R-744 based water heating heat pumps have been mainly developed and commercialised in Japan. However, the expansion of this technology to other countries is limited by its high cost. R-717 has also been used in a small number of reversible heat pumps and absorption heat pumps.
